I plan on slapping a set of L98 aluminum heads on my L69 (until I can afford a short block 350). I will be using a hydraulic cam & lifters. The aluminum L98s are 58cc, so I will have the same 9.5:1 or whatever compression with my stock flattop pistons. My question is for those of you who have made this swap. What head gasket thickness did you use, and what is the max lift everyone has experienced without a valve hitting the block or piston? I'll also be installing a Performer intake and headers, as well as port matching & polishing the heads and intake. How much of a gain do you think I'll see? Desktop Dyno 2000 shows approximately 300HP@5000RPM and 350FT/LBS@4000RPM.

 

You should use a gasket made for aluminum heads, its probably going to be thicker than stock, like .039 rather than the .016 or 18 or 20 or whatever the factory gasket is, I cant remember exactly.
I dont think you will have any problems with lift unless the valves have been changed to something bigger than stock.